Method for controlling an automatically operated motor vehicle transmission

ABSTRACT

A method for controlling an automatically actuated transmission for a motor vehicle, for improving behavior before curves and during braking, provides that a coasting function to suppress a shift or gear ratio changing process is initiated as soon as the accelerator pedal is quickly released. This coasting function is maintained until powered operation is again detected and the vehicle accelerates. Then a holding time is started during which the coasting function is started again as soon as the vehicle changes to coasting operation. 
     The method is applicable to multi-step transmissions as well as continuously variable transmissions.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to application Ser. No. 08/170,184 filed onDec. 21, 1993 in the name of Joseph PETERSMANN et al. for METHOD OFCONTROLLING A CONTINUOUSLY VARIABLE TRANSMISSION, now pending.

The invention relates to a method according to the species of the mainclaim.

In conventional automatic transmission controls of motor vehiclespowered by internal combustion engines, when the accelerator pedal isreleased, because of the reduced load signal (throttle aperture angle)at approximately the same driving speed, as a rule initiate a reductionof the gear ratio or an upshift. This is not always desirable, however,when rounding curves or when braking, since load changes of this kindunder certain conditions may lead to unsafe driving states, or when themotor vehicle is being accelerated again by pressing harder on theaccelerator and an increase in the gear ratio or a downshift must beforced. This effect is independent of the transmission design and occursin both multi-step transmissions and in continuously variabletransmissions.

In DE 33 41 652 C2, in the latter and in connection with automaticallyshifted multi-step transmissions, it is proposed to prevent thisreduction of the gear ratio (upshifts) on curves by detecting thetransverse acceleration of the motor vehicle. However, this can only beused to avoid shifting on curves.

EP 00 93 312 A1 teaches a method and a device for adjusting the gearratio of a continuously variable transmission in which, to increase theengine braking effect, it is proposed to keep the gear ratio constantfor a certain period of time when the accelerator is released rapidly.If a minimum speed is undershot before this time elapses, or the brakeis actuated, or the throttle reaches its neutral position, maintenanceof the constant state is interrupted.

In order to be able to prevent a reduction of the gear ratio even whenapproaching curves, in the method for controlling an automaticallyshifting transmission according to DE 39 22 040 A1 the rate of change inthe accelerator pedal is detected and, when a certain (negative)boundary value is undershot, the signal to suppress an upshift processis derived as soon as coasting is detected. Then upshifts are suppresseduntil power is applied again and a fixed time interval has elapsed.

It is also provided in DE 39 22 051 A1 to make this time intervaldependent upon another parameter (driving activity), which is derivedfrom one or from a combination of several operating and/or drivingparameter(s) of a motor vehicle and evaluates a driving style of adriver or a traffic situation prevailing at the moment.

On the basis of this prior art, it is the goal of the invention toprovide a method for controlling an automatically operated transmissionfor a motor vehicle, which in particular is improved further as regardsbehavior ahead of curves and during braking and which can be used bothfor multi-step transmissions and for continuously variabletransmissions.

The goal is achieved according to the invention by the characterizingfeatures of claim 1. Additional features that characterize the inventionare contained in the subclaims.

The advantages of the invention lie primarily in the fact that a methodfor controlling an automatically actuated continuously variabletransmission for a motor vehicle is provided in which the adjustmentbehavior ahead of curves and during braking is further improved andwhich is usable both for multi-step transmissions and for continuouslyvariable transmissions. A coast function to suppress a shifting or gearratio changing process is initiated as soon as the accelerator pedal isreleased rapidly. This coast function is maintained until theapplication of power is detected once more and the vehicle accelerates.Then a holding time is started during which the coast function isstarted again as soon as the vehicle begins coasting.

During coasting, the gear ratio set when the function was initiated ismaintained and the gear that was engaged when the function was initiatedis maintained. In the case of a continuously variable gear ratio, it ispossible to provide, as an alternative, for the shift to take place at arelatively low speed or to be set so that the engine rpm changes at alow speed.

After the holding time has expired, in a continuously variabletransmission the shift is adjusted by means of a transition function tothe set point determined by shift curves from the currently prevailingoperating conditions, in order to avoid abrupt changes. The transitionfunction for example can be a filter with a degressive, linear, orprogressive nature or a first or second order delay element, and thattime behavior can be freely adjustable. If coasting is again detectedduring the transition function, the coast function is started again. Inmulti-step transmissions, after the holding time has expired, a shift byone gear in the direction of a set gear predetermined by a shift diagramis permitted and the holding time started again. This is repeated untilthe set gear is reached.

This ensures that brief acceleration does not result in suspension ofthe constantly maintained state or in a slow change in the gear ratio.This can occur for example when the driver has falsely estimated theengine braking torque that develops when he releases the acceleratorpedal quickly, and tries to compensate for this.

This coast function can also be initiated with a downshift functionwhich, when noncritical conditions prevail during braking, initiates adownshift or an increase in the gear ratio. If these noncriticalconditions are no longer all met, the coast function according to theinvention is called up.

Maintenance of noncritical conditions thereby ensures safe operation ofthe motor vehicle. Thus monitoring is performed to ensure in particularthat the transverse acceleration is not too high, the vehicle is notbeing decelerated too sharply, and the driving speed is not too high, inorder to avoid loss as a result of the longitudinal and lateral guidingforces on the wheels of the motor vehicle. The braking torque of thedriving (internal combustion) engine which acts on the drive wheelsfollowing an increase in the gear ratio or a downshift can therefore nothave a negative effect on the driving behavior of the motor vehicle.

Increasing the gear ratio or downshifting when braking firstly increasesthe braking effect of the engine of the motor vehicle during coasting,so that the brake (service brake) of the motor vehicle has the load onit reduced. On the other hand, in conjunction with maintenance of or aslow change in the gear ratio ahead of, in, and beyond curves, it isensured that the driver always has available to him, after rounding acurve, the optimum gear ratio and engine rpm for re-accelerating themotor vehicle.

To avoid vehicle instability caused by excessive slip at the drive axle,the coast function is disconnected or interrupted when slip appears, bya slip monitoring function which instead increases the gear ratio orinitiates a stepwise upshift until the slip is in the permissible range.When a holding time thus started has expired and the vehicle isaccelerating, the slip monitoring function ends.

The invention will be described below with reference to the embodimentsshown in the drawings.

FIG. 1 is a block diagram of an electrohydraulic control for acontinuously variable transmission of a motor vehicle;

FIG. 2 is a family of several control curves which allocate specificvalues of engine rpm setpoints to the values of the throttle angle;

FIG. 3 is a boundary curve for recognition of accelerating/coastingoperation;

FIG. 4 is a first and a second driving-speed-dependent boundary curvefor a transverse acceleration;

FIG. 5 is a characteristic diagram for a value that is dependent uponengine rpm and gear ratio;

FIG. 6 is a characteristic diagram for a factor that depends upon thegear ratio and driving activity, and

FIG. 7 is a curve showing the dependence of holding times upon a drivingactivity.

In FIG. 1, 1 represents a control for an electrohydraulically actuatedcontinuously variable transmission 2 using the example of a frictiontransmission. Continuously variable transmission 2 is driven through acontrollable engaging clutch 3 by an internal combustion engine 4. Adrive shaft 5 of continuously variable transmission 2 is connected witha wheel drive, not shown, of a motor vehicle.

In the following, the signals that change with time t are shown asfunctions f(t) of time.

A control device 6 controls a hydraulic valve body 9 at least as afunction of the (without limiting the general nature) throttle positionalpha(t) of a throttle sensor 7 and the actual value of an engine rpmnmot(t) of an engine rpm sensor 8 of internal combustion engine 4. Ofcourse, instead of the position of the throttle, the position of anyelement that influences the driving power of a driving engine of a motorvehicle, for example an accelerator pedal or an injection pump lever ofan autoignition diesel engine or the output signal from an electrical orelectronic accelerator pedal, can be detected and processed.

To control continuously adjustable transmission 2 and engaging clutch 3,control device 6 receives as additional input values or measured values,the air volume or air mass ml(t), supplied to the internal combustionengine, from an air-volume or air-mass sensor 12 as well as thetransmission input rpm ne(t) of a transmission input rpm sensor 13 and adriving speed v(t) of a driving speed sensor 14 of the motor vehicle. Inaddition, a speed vref(t) of a reference speed sensor 15 on a non-drivenvehicle axle and a transverse acceleration aq(t) of a transverseacceleration sensor 16 are detected and processed by control device 6.

Finally the control is usually controllable by the vehicle driver by aselector lever 18 to preselect gears: P (park), R (reverse), N(neutral), and D (automatic adjustment of the gear ratio ue of thecontinuously variable transmission); in addition, an adjustment range ofselector 18 is provided for directly selecting the gear ratio ue.

In ordinary transmission controls, the control curve according to whichcontrol device 1 in position D controls the continuously variabletransmission, is selected. As a rule, two control curves can be selectedwhereby in the E position a control curve RKL1 optimized for economy,and in position S a control curve RKL5 optimized for performance, can beset manually.

Alternatively to program selector 19, a control method canadvantageously be implemented in control device 6, which, for exampleaccording to DE 33 48 652 C2 or DE 39 22 051 A1, evaluates the drivingstyle of a driver or his behavior as a function of traffic situationsrelative to the control of the motor vehicle and derives a drivingactivity SK(t) (accelerator pedal activity) from one or more operatingor driving parameters. On the basis of this driving activity SK(t),depending on the shift position of program selector 19, one of severalof control curves RKLj=f(SK(t)); (j=1, 2 , . . . , 5), referred tohereinafter as RKL(SK), is then used to control the continuouslyvariable transmission or engaging clutch 3.

Depending on the values mentioned above, control device 6, through asignal output pk and valve body 9, controls the hydraulic pressure inengaging clutch 3 and, through signal outputs pe and pa and hydraulicvalve body 9, controls the gear ratio. The gear ratio ue(t) here isproportional to the quotient of the transmission input rpm ne(t) and thedriving speed v(t): ue(t)=prop,(ne(t)/v(t)); here prop is a proportionalfactor.

Here and in the following, these definitions apply:

an upshift in a multi-step transmission corresponds to a decrease in thegear ratio ue or a reduction of the engine rpm nmot (t) and

a downshift in a multi-step transmission corresponds to an increase inthe transmission ratio ue or an increase in the engine rpm nmot(t).

Hydraulic valve body 49 connects the corresponding control lines 20, 21,and 22 of engaging clutch 3 and continuously variable transmission 2with a pressure line 24 connected to a pump 23 or to a return line 25 toa supply tank 26 for hydraulic fluid.

To control continuously variable transmission 2, the gear ratio ue ofthe transmission is set automatically by means of control device 6 andvalve body 9 through control curves RKL(SK) at least as a function ofthe throttle position alpha(t) and the engine rpm n(t); the controlcurve RKL(SK) is then selected as a function of the switch position ofprogram selector 19 or the driving activity SK(t) of the driver or hisbehavior as a function of traffic situations relative to the control ofthe motor vehicle, from a family of several control curves RKL(SK) (j=1,2 , . . . , 5) corresponding to FIG. 2.

Without limitation of the general nature, other parameters can also beused to control the continuously variable transmission or the controlcurves can be expanded to control curve diagrams or characteristicdiagrams.

The control curves shown in FIG. 2 cover the area between a controlcurve RKL1 that permits a type of operation of the motor vehicle whichis optimized for consumption (position "E" of the program selector) anda control curve RKL5 with which the motor vehicle can be operated withmaximum performance (position "S" on program selector 19), at least insteps.

As soon as the control undertakes the selection of the control curvesRKL(SK) as a function of driving activity SK(t), the control ofcontinuously variable transmission 2 automatically adjusts to thedriver's driving style so that no manual intervention or adjustment ofthe control curves need be performed.

The gear ratio ue of continuously variable transmission 2 is preferablyadjusted by control device 6 in such a way that the engine rpm nmot(t)is adjusted as optimally as possible to an engine rpm setpoint nmots.For this purpose a subordinate rpm governor can be provided in controldevice 6. Gear ratio ue is therefore a function of engine rpm setpointnmots, engine rpm nmot, and time t: ue=f(nmots, nmot, t). A variationDnmot(t)=nmots(t)-nmot(t) of the engine rpm nmot(t) from engine rpmsetpoint nmots(t) is brought toward 0.

The current value of engine rpm setpoint nmots is then determined bymeans of the control curve RKL(SK) assigned to the momentary drivingactivity SK(t) according to FIG. 2 from the current value of thethrottle position alpha(t): nmots=RKL(SK)(alpha, SK).

As we can see from FIG. 2, control curves RKL(SK) essentially have aprogressive pattern in a lower value range of the throttle positionalpha, which merges in a central area of the throttle setting alpha intoa degressive curve. Throttle position alpha is plotted on the horizontalaxis in percent, with the value 0% corresponding to a closed throttle,i.e. the neutral position, and the value 100% corresponding to afully-opened throttle.

Five control curves are plotted, RKL1, RKL2, RKL3, RKL4, and RKL5, withcontrol curve RKL1 permitting consumption-optimized operation of themotor vehicle and being selected for minimum driving activitySK(t)=SKmin. Control curve RKL5 is selected for maximum driving activitySK(t)=SKmax, at which performance-optimized operation of the motorvehicle is possible.

Corresponding to DE 33 41 652 C2 or DE 29 22 051 A1, driving activitySK(t) is determined by a functional relationship that evaluates thedriving style of the driver or his behavior as a function of trafficsituations in the long term, from cyclically or anticyclically detectedcurrent and past values of a single operating parameter or at a singlevalue assembled from several operating parameters of a motor vehicle.

For this purpose, for example, values of the throttle position alpha(t),driving speed v(t), and transverse acceleration aq(t) in the millisecondrange were collected and from them, additional values such as forexample the throttle change rate dalpha(t)/dt and theacceleration/deceleration of the vehicle dvt(t)/dt were calculated. Thevalues obtained and calculated were linked by characteristic diagramswith other operating parameters and combined by a functionalrelationship into an intermediate parameter from which a drivingactivity SK(t) was obtained by sliding averaging which takes intoaccount both the newly calculated values and the past values over thelong term.

By means of another functional relationship, a control curve RKL(SK) isassigned to this driving activity SK(t), for example corresponding tothe manner shown in DE 39 22 051 A1.

A rapid coast phase, as shown previously in DE 39 22 040 A1 and DE 39 22051 A1, can be recognized when the change in throttle position as afunction of time dalpha(t)/dt is sensed. As a rule, a driver, forexample before entering a curve, lets up on the accelerator, and, as arule on the throttle as well, more rapidly than he does under normalcircumstances in order to adjust the driving speed for example.

This initiates a coast function during which the gear ratio set at themoment of function initiation is maintained.

The coast function ends when the vehicle changes to power applicationand is accelerated, and a holding time T1 started when these twoconditions apply has expired. If coasting operation of the vehicle isrecognized within this holding time T1, the coast function is triggeredagain.

After the coast function has ended, the gear ratio ue is adjusted sothat the engine rpm setpoint nmots(t) provided on the momentarilyadjusted control curve RKL(SK) at the momentary operating point of themotor vehicle (alpha(t), v(t), nmot(t), t) is reached. If coastingoperation of the vehicle is detected during the adjustment, the coastfunction is triggered again.

To identify the coast phase, the change in throttle position with timeis compared with a limiting value which in turn can depend on thedriving activity: dalpha(t)dt/<dalpha, grenz (SK). The dependence upondriving activity takes into account the fact that change in the throttlewith time, on the average, is greater with performance-optimizeddriving, corresponding to SK=5, than for consumption-optimizedoperation, corresponding to SK=0.

To determine whether the vehicle is accelerating, a longitudinalacceleration al(t)=dvref(t)/dt is formed from speed vref(t) and comparedto determine whether the latter is greater than 0: al(t)>0 m/s².

Holding time T1 is largely dependent on driving activity SK(t), but itcan also be dependent on the gear ratio set: T1=f(SK(t), ue(t)).

The terms "powered operation" and "coasting operation" refer to thesystem in question. The following distinctions are made:

Total motor vehicle system: in powered operation the acceleration of themotor vehicle (change in driving speed with time) is dv(t)/dt>0, whilecoasting operation corresponds to a deceleration of the motor vehicledv(t)/dt<0.

Clutch/transmission system: in powered operation, the input rpm of theclutch (torque converter)/transmission system is greater than its outputrpm, while in coasting operation the input rpm is smaller than theoutput rpm.

Internal combustion engine system: powered operation means a throttleposition alpha(t)>0 and a change in engine rpm with time dnmot(t)/dt>0,while in coasting operation the throttle setting is alpha(t)=0 or thechange in engine rpm with time dnmot(t)/dt<0.

In the case of transmission control as well as the overall behavior ofthe motor vehicle, it has been found to be advantageous to simulate theterms "powered operation" and "coasting operation" as follows:

Coasting operation is recognized when the throttle position alpha(t)drops below an engine rpm-dependent boundary curve azsg(nmot), as shownin FIG. 3: alpha(t)<azsg(nmot).

Powered operation is recognized when the throttle position alpha(t)exceeds the engine rpm-dependent boundary curve azsg(nmot) according toFIG. 3, and the change in driving speed as a function of time dv(t)/dtassumes positive values: (alpha(t)>azsg(nmot) and dv(t)/dt>0).

The adjustment of the engine rpm nmot(t) to the engine rpm setpointnmots(t) is accomplished by a transition function by which an abruptchange in engine rpm nmot(t) is avoided. The transition function can bea linear, degressive, or progressive filter, but can also take the formof a deceleration element of first or second order. Parameters of thetransition function are chosen to be dependent upon driving activity.The transition function ends when the deviation of the engine rpm andnmot(t) from the engine rpm setpoint nmots(t) drops below a presetthreshold.

Under certain noncritical conditions, to increase the engine brakingeffect, it is also provided to increase the gear ratio ue (correspondingto a downshift) by means of a change in the gear ratio that is predictedby a characteristic diagram and depends upon the vehicle deceleration.

For this, the following are both necessary:

a) the vehicle must be in coast operation and

b) a transverse acceleration aq(t) detected by transverse accelerationsensor 17 must be below a certain first driving speed-dependenttransverse acceleration boundary line aqg1(v(t)): aq(t)<azg1(v(t), and

c) the change in driving speed with time dv(t)/dt must be less than asecond negative longitudinal acceleration boundary value albbg(nmot, ue,SK(t), t)=k(ue, SK(t))*albg(ue, nmot, t): dv(t)/dt>albbg(nmot, ue,SK(t), t), and

d) the driving speed v(t) must be below a driving speed limiting valuevg(ue, SK(t)): v(t)<vg(ue, SK(t)).

If these conditions are no longer met the coast function is activated.

Here are the conditions in detail:

a): The first negative longitudinal acceleration boundary value albg(ue,nmot, t) depends on the momentary values of the gear ratio ue and theengine rpm nmot(t) and here corresponds to the respective (negative)longitudinal acceleration dv/dt (and hence the deceleration) of a motorvehicle rolling on a flat road in a defined state (load, tire pressure,environmental conditions, etc.) with a closed throttle alpha=0, with therespective value pairs of the momentarily set gear ratio ue and enginerpmnmot(t).

The first negative longitudinal acceleration boundary value albg(ue,nmot, t) is determined from the momentary values of these parameterspreferably by means of a first characteristic diagram ALB(ue, nmot):albg(ue, nmot, t)=ALB(ue, nmot). An example of such a firstcharacteristic diagram ALB(ue, nmot) is shown in FIG. 5. Here forexample are four gear ratio-dependent curves that represent, for certaincharacteristic diagram values ALB(ue, nmot) in unit g, the specificvalues of the engine rpmnmot (in revolutions per minute) correspondingto 9, 81, . . . meters per second (acceleration of gravity).

The values 2.48-1.48-1.0-0.73 are plotted as gear ratios. To determinethe characteristic diagram values of the vehicle-specific characteristicdiagram that differ from the (gear ratio) curves shown, it is possibleeither to interpolate or extrapolate as a function of the gear ratio inknown fashion. Alternatively of course the longitudinal accelerationboundary values albg(g, nmot, t) can also be determined using acorresponding functional relationship.

The curves in FIG. 5 clearly show the dependence of the decelerationvalues of a motor vehicle with an internal combustion engine upon gearratio ue and engine rpm nmot(t). For increasing values of engine rpmnmot(t) the deceleration values are greater because of the increasingengine braking effect and the increasing rolling resistance and airresistance of the vehicle. Likewise, the deceleration values rise as thegear ratio ue becomes greater, since the braking torque of the internalcombustion engine, because of the higher gear ratio, has a greatereffect on the deceleration rate of the motor vehicle.

b): The first transverse acceleration boundary line aqg1(v(t)) ispreferably driving-speed dependent. A corresponding curve is shown inFIG. 4. It takes into account the fact that the gear ratio ue is onlyincreased when the transverse acceleration of the motor vehicle is nottoo high.

Checking to determine whether the transverse acceleration aq(t) is belowthe first specified transverse acceleration boundary line aqg1(v(t))monitors whether the vehicle is not already in a--relatively tight orrapidly traveled--curve. If such a curve travel is already present, theincrease in the gear ratio (corresponding to a downshift) is suppressed,so that the frictional connection between the wheel and the road is notlost because of the braking action that would otherwise increase.

c): The second negative longitudinal acceleration boundary valuealbbg(nmot, ue, SKt))==k(ue, SK(t))*albg(ue, nmot, t) is determined froma product of a gear-ratio-dependent factor k(ue, SK(t)) and a value forthe first longitudinal acceleration boundary value albg(ue, n/not, t)which is determined for the momentary operating conditions of the motorvehicle.

The gear-ratio-dependent factor k(ue, SK(t)) is determined with a secondcharacteristic diagram k(ue, SK(t))=F(ue, SK(t)) from the momentary gearratio ue. An example of the second characteristic diagram will be foundin FIG. 6. Here again gear-ratio-dependent curves (gear ratios2.48-1.48-1.0-0.73) indicate the values of driving activity SK(t),dimensionless values of the factor k(ue, SK(t)); the characteristicdiagram values valid for gear ratio values that differ from this can inturn be calculated by interpolation or extrapolation from the availablevalues.

Monitoring the exceeding of the second negative longitudinalacceleration boundary value albbg(nmot, g, SK(t)), i.e. of a secondminimum vehicle deceleration, constitutes a safety function; this is adetermination of whether the higher deceleration of the motor vehiclethat would be expected as a result of the increase in the gear ratio ue(corresponding to a downshift) would lead to exceeding the adhesivefriction limit of the wheels.

For this purpose, a momentary maximum permissible deceleration isobtained from the deceleration anticipated at the momentary drivingstate by weighting (multiplication) with the gear-ratio-dependent factork(ue, SK(t)) and this is compared with the momentary vehicledeceleration dv(t)/dt; if the momentary deceleration is higher, anincrease of the gear ratio (corresponding to a downshift) is suppressed.

The gear-ratio-dependent factor k(ue, SK(t)) takes into account the factthat the second negative longitudinal acceleration (vehicledeceleration) limiting value albbg(ue, nmot, t) is smaller than thefirst longitudinal acceleration boundary value albg(ue, nmot, t) and istherefore larger in value (corresponding to a higher deceleration rate).

d): The driving speed boundary value vg(ue, SK(t), t) depends on thegear ratio ue and the driving activity SK(t).

With monitoring of the exceeding of the gear-ratio-dependent drivingspeed boundary value vg(ue, SK(t), t), additional safety criteriaregarding an increase in the gear ratio (corresponding to a downshift)at too high a driving speed or the prevention of exceeding rpm limits ofthe driving internal combustion engine after increasing the gear ratioare met. These safety criteria are highly vehicle specific and musttherefore be adjusted individually to each vehicle, so that showing acorresponding characteristic diagram is superfluous.

In order to avoid an undesired change in the gear ratio ue whilerounding a curve, after approaching curves or braking before curves, thetransverse acceleration of the motor vehicle is monitored. The gearratio ue is maintained as long as the amount of transverse acceleration|aq(t)| is above a second and lower transverse acceleration boundaryline aqg2(v(t)) that depends on the driving speed v(t) as shown in FIG.4 or as long as a holding time T2(SK(t)) has not yet elapsed afterundershooting the transverse acceleration boundary line aqg2(v(t)). Ifthe transverse acceleration boundary line aqg2(v(t)) is exceeded againduring holding time T2(SK(t)), the function is restarted. If, afterholding time T(SK(t)) has expired, powered operation is detected and thevehicle accelerates, the gear ratio is maintained for an additional timeT3(SK(t)). If this is not the case or the holding time T3(SK(t)) hasexpired, the engine rpm nmot(t) is adapted to the engine rpm setpointnmots(t) by means of a transition function in the manner describedabove.

On a higher level, a slip-monitoring function prevents possibleinstability as a result of excessive slip at the drive axle while thegear ratio is increased in order to reduce the torque acting on thedrive axle. This function can interrupt or prevent the functionsdescribed earlier.

The slip-monitoring function is triggered when the difference Dv(t)between a speed vref(t) of a non-driven axle and the driving speed v(t)recorded from a driven axle exceeds a first permissible differentialspeed value Dvzul1(SK)t)): Dv(t)>Dvzul1(SK(t)).

The slip-monitoring function begins adjusting the gear ratio ue in suchfashion that a predetermined very small engine rpm and hence a smallengine torque are reached. This change in gear ratio is interrupted assoon as the difference Dv(t) corresponding to slip drops below a seconddifferential speed value Dvzul2(SK(t)): Dr(t)<Dvzul2(SK(t)).

If this condition is met, a holding time T4(SK(t)) is started withinwith the slip-monitoring function is triggered again by recognition ofslip.

The slip-monitoring function ends when the vehicle is in poweredoperation, is being accelerated, and the holding time has elapsed.

In addition, to reduce excessive wheel slip within the slip-monitoringfunction, the controllable engaging clutch 3 is opened completely orpartially.

Likewise, monitoring functions are provided to prevent racing orstalling of the internal combustion engine.

The holding times T1(SK(t)), T2(SK(t)), T3(SK(t)), and T4(SK(t)) areindependent of one another, and like the driving speed boundary valuevg(ue, Sk(t), t) or the gear-ratio-dependent factor k(ue, SK(t)) can beadjusted at will. Preferably they are adjusted together with anadjustment of the control curves RKL(SK)(consumption-optimized drivingprogram, control curve RKL1; performance-optimized driving program,control curve RKL5) in such manner that for more performance-optimizeddriving programs (control curve RKL5) the holding times T1(SK(t)),T2(SK(t))), T3(SK(t)), T4(SK(t)) and the boundary value vg(g, SK(t), t)grow larger, and the gear-dependent factor k(g-1, SK(t)) and thepermissible differential speed value Dvzul(SK(t)) become smaller.

If on the other hand the transmission control provides for automaticadjustment of the control curves (RKL(SK)) corresponding to the drivingactivity (SK(t)) that evaluates the driving style of the driver or hisbehavior as a function of a traffic situation relative to the control ofthe motor vehicle in the long term, the holding times T1(SK(t)),T2(SK(t)), T3(SK(t)), T4(SK(t), the driving speed limiting value vg(ue,Sk(t), t), the gear-ratio-dependent factor k(ue, SK(t)) or thepermissible differential speed value Dvzul(SK(t)) can also directlydepend in part or completely on driving activity SK(t). With an increasein driving activity SK(t) which is more performance-oriented, preferablythe holding times T1(SK(t)), T2(SK(t)), T3(SK(t)), T4(Sk(t)), and theboundary value vg(g, SK(t), t) grow larger and the gear-dependent factork(g-1, SK(t)) and the permissible differential speed value Dvzul (SK(t))become smaller.

The embodiment shown can be transferred analogously to a multi-steptransmission. Instead of the control curves RKL(SK), there are thenshift programs and shift diagrams.

Instead of the transition function there is then a shift by one gear ata time followed by a holding time during which the function from whichthe transition takes place can be restarted.

In the case of a downshift to increase the engine braking effect it isnecessary, in addition to the above-mentioned conditions, for the changewith time of the driving speed dv(t)/dt to be below the first negativelongitudinal acceleration boundary value albg(g, nmot), dv(t)/dt<albg(g,nmot), in other words a minimum vehicle deceleration is reached. Fromthis, the driver's wish is derived after increased deceleration of thevehicle or after an increase in the gear ratio (corresponding to adownshift).

This function produces a downshift by one gear. Then no furtherdownshifts are made for a waiting time T5(SK(t)). After waiting timeT5(SK(t)) has expired, the coast function is activated.

The slip-monitoring function is triggered by the same criteria but inaddition to opening a converter bridge coupling, produces an upshift byone speed followed by prevention of shifts for a holding time T6(SK(t)).During this holding time T6(SK(t)) the reaction of the vehicle tomeasures taken is checked; if there is still slip after this time hasexpired, further upshifts are conducted with a new holding time.

The higher-order monitoring functions are likewise provided formulti-step transmissions.

On the other hand, it is only in continuously variable transmissionsthat, as an alternative to keeping the gear ratio constant, adjustingthe latter with less speed is provided. The shifting process can beregulated or controlled through the gear ratio ue or the engine rpmnmot(t), in other words either the gear ratio ue or the engine rpmnmot(t) is brought back to the value determined by the current operatingpoint according to a desired curve.

We claim:
 1. Method for controlling an automatically operatedtransmission of a motor vehicle, especially one powered by an internalcombustion engine, whose internal combustion engine can be influenced bya performance control element, with the gear ratio (ue) or the gear oftransmission being adjusted automatically by at least one characterizingcurve (RKLj) at least as a function of the throttle position (alpha(t))and the engine rpm (nmot(t)), wherein the gear ratio (ue) or the gear ofthe transmission is kept constant when a change with time (dalpha(t)/dr) of the throttle position (alpha (t)) falls below a negativeboundary value (-alphaga), and a holding time (Ti(SK(t))) that beginsafter the vehicle begins to accelerate has not yet expired, whereby inthe case that coasting operation is again detected during the expirationof holding time (T1(SK(t)))bm, the gear ratio /ue) is one of keptconstant and slowly adjusted until accelerated operation is againdetected and the holding time (T1(SK(t))) has again elapsed.
 2. Methodaccording to claim 1 characterized by the fact that coasting operationis detected when the throttle position (alpha(t)) drops below a boundarycurve (azsg(nmot)) that is dependent on the engine rpm(alpha(t)<azsg(nmot)).
 3. Method according to claim 1 characterized bythe fact that coasting operation is recognized when the throttleposition (alpha(t)) exceeds the engine rpm-dependent boundary curve(alpha(t)>azsg(nmot)) and the change with time in driving speed(dv(t)/dt) assumes positive values (alpha(t)>azsg(nmot) and dv(t)/dt>0.4. Method according to claim 3 characterized by the fact that afterexpiration of holding time (T1(SK(t))) adjustment of the engine rpm tothe engine rpm setpoint is accomplished by changing the gear ratio (ue)with the aid of a transition function.
 5. Method according to claim 4characterized by the fact that the transition function is a filter withdegressive, linear, or progressive character or a delay element of firstor second order, whose parameters are freely adjustable.
 6. Method forcontrolling an automatically operated transmission of a motor vehicle,especially one powered by an internal combustion engine, whose internalcombustion engine can be influenced by a performance control element,with the gear ratio (ue) or the gear of transmission being adjustedautomatically by at least one characterizing curve (RKLj) at least as afunction of the throttle position (alpha(t)) and the engine rpm(nmot(t)), wherein when a first condition representative of coastingoperation and slight transverse acceleration and sufficient distancefrom the limit of adhesive friction and sufficient distance from maximumspeed is present and in multi-step transmissions a second conditionrepresentative of reaching a minimum deceleration in continuouslyvariable transmissions initiates an increase in the gear ratio up to atravel-speed-dependent limiting value and, in multi-step transmissions,a downshift by one gear is initiated, and then, for a waiting time, thegear ratio or gear is determined until a holding time (T1(SK(t))) thatbegins after acceleration operation begins, has elapsed, whereby in thecase where a new coasting operation is detected during expiration of theholding time (T1(SK(t))), the gear ratio continues to be one of keptconstant and slowly adjusted until accelerated operation is recognizedagain and the holding time (T1(SK(t))) has once again elapsed.
 7. Methodaccording to claim 6 characterized by the fact that after the waitingtime the gear ratio or the gear can be kept constant only when the firstcondition and in multi-step transmissions the second condition are nolonger met.
 8. Method according to claim 7 characterized by the factthat the difference (Dv(t)) between a driving speed (vref(t)) and aspeed determined on a driven axle (v(t)) is constantly monitored, andwhen an admissible differential value (Dvzul1(t)) is exceeded, the gearratio is increased or upshifted by one gear until difference (Dv(t))drops below a second differential value (Dvzul2(t)).
 9. Method accordingto claim 8 characterized by the fact that simultaneously a positiveconnection between the engine and the transmission is completely orpartially broken.
 10. Method according to claim 9 characterized by thechange in the gear ratio or the gear is ended when the vehicle is inpowered operation and being accelerated.
 11. Method according to claim10 characterized by the fact that at least one of the holding times orone of the boundary values or one of the comparative values or one ofthe factors is arbitrarily adjustable and preferably can be set togetherwith an adjustment of the characterizing curves (RKLj)(consumption-optimized driving program, control curve RKL1;performance-optimized driving program, control curve RKL5) in suchfashion that with the more performance-optimized driving program(control curve RKL5) the holding times and the boundary values increaseand the comparison values or factors decrease.
 12. Method according toclaim 10 characterized by the fact that at least one of the holdingtimes or one of the boundary values or one of the comparison values orone of the factors depend upon the driving activity (SK(t)) evaluatingthe driving style of the driver or his behavior in traffic situationsrelative to the control of the motor vehicle in the long term and, withincreasing, more performance-oriented driving activity (SK(t)), theholding times and the boundary values increase and the comparison valuesor the factors decrease.
 13. Method according to claim 12 characterizedby the driving activity (SK(t)) being determined by a functionalrelationship (sliding averaging) which evaluates the driving style ofthe driver or his behavior in traffic situations relative to the controlof the motor vehicle on a long-term basis, from current and past valuesof a single operating parameter or a parameter assembled from severaloperating parameters of a motor vehicle.